U.S. patent number 7,696,762 [Application Number 12/147,227] was granted by the patent office on 2010-04-13 for non-metallic flow-through electrodeless conductivity sensor and leak detector.
This patent grant is currently assigned to Invensys Systems, Inc.. Invention is credited to Michael M. Bower, Donald S. McKinlay, John Kevin Quackenbush, Stephen B. Talutis.
United States Patent |
7,696,762 |
Quackenbush , et
al. |
April 13, 2010 |
Non-metallic flow-through electrodeless conductivity sensor and
leak detector
Abstract
A non metallic flow through electrodeless conductivity sensor is
provided with a conduit having primary and secondary process fluid
flowpaths to form a fluid loop. At least one drive and one sense
toroid surround the conduit on the fluid loop. Voltage supplied to
the drive toroid induces a current in the sense toroid via the
fluid loop to eliminate any need for metallic electrodes in contact
with the process fluid. At least one additional drive and/or sense
toroid is disposed on the fluid loop to enhance induction.
Optionally one or more sense coils are disposed about the conduit
outside of the fluid loop to cancel out stray electrical noise. An
optional conductor disposed along the conduit detects any fluid
leakage through changes in resistance thereof.
Inventors: |
Quackenbush; John Kevin
(Middleboro, MA), Bower; Michael M. (Wareham, MA),
Talutis; Stephen B. (Milton, MA), McKinlay; Donald S.
(Wareham, MA) |
Assignee: |
Invensys Systems, Inc.
(Foxboro, MA)
|
Family
ID: |
46045527 |
Appl.
No.: |
12/147,227 |
Filed: |
June 26, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080258735 A1 |
Oct 23, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11351856 |
Feb 9, 2006 |
7405572 |
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60676765 |
May 2, 2005 |
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Current U.S.
Class: |
324/696; 324/693;
324/446 |
Current CPC
Class: |
G01N
27/023 (20130101); Y10T 29/49002 (20150115) |
Current International
Class: |
G01N
27/02 (20060101); G01R 27/08 (20060101) |
Field of
Search: |
;324/696,693,439,446 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Derwent Abstract of JP2001147218A2: Electrodeless Sensor (2 Pgs.).
cited by other.
|
Primary Examiner: He; Amy
Attorney, Agent or Firm: Sampson & Associates P.C.
Parent Case Text
RELATED APPLICATION
This application is a divisional of U.S. patent application Ser.
No. 11/351,856 entitled Non-Metallic Flow-Through Electrodeless
Conductivity Sensor and Leak Detector, filed on Feb. 9, 2006 now
U.S. Pat. No. 7,405,572 which claims priority to U.S. Provisional
Patent Application Ser. No. 60/676,765 entitled Non-Metallic Flow
Through Electrodeless Conductivity Sensor, filed on May 2, 2005.
Claims
Having thus described the invention, what is claimed is:
1. An electrodeless conductivity sensor for determining
conductivity of a process fluid, said sensor comprising: An
electrically non-conductive conduit for the flow of a process
fluid, said conduit having an inlet and an outlet; said conduit
diverging downstream of the inlet into first and second legs, said
legs re-converging upstream of said outlet, to form a fluid-flow
loop between said inlet and said outlet; at least one first toroid
configured as a first type coil disposed about one of said first
and second legs; at least one second toroid configured as a second
type coil disposed about one of said first and second legs; at
least one third toroid configured as a redundant one of said first
or second type coils disposed about one of said first and second
legs; wherein coils of the same type are disposed on opposite legs,
in co-planar orientation with one another; said first type and
second type coils selected from the group consisting of drive and
sense coils; at least one other sense coil disposed about said
conduit outside of said fluid loop; and a connector configured to
couple said first, second and third toroids to an analyzer.
2. The sensor of claim 1, wherein said at least one other sense
coil is connected electrically out of phase with sense coils
disposed on said first and second legs.
3. The sensor of claim 1, further comprising: a housing enclosing
said first and second legs; a plurality of toroids of first and
second types surrounding each of said first and second legs; at
least one toroid of said first type disposed between toroids of
said second type on each of said first and second legs; wherein
said device is configured for use in a non-metallic fluid flow
system; shields interspersed between said coils, configured to
magnetically isolate said coils from one another; a calibration
loop including an electrical conductor extending through said
plurality of toroids; and a leakage detector including an other
electrical conductor disposed within said housing in spaced
relation from said plurality of toroids, said leakage detector
connectable to resistance measuring means.
4. The sensor of claim 1, further comprising: an electrical
conductor disposed in leakage-contacting relation to the conduit;
said conductor having a predetermined electrical resistance; a test
port having terminals coupled to opposite ends of said conductor;
said test port being couplable to resistance measuring means for
measuring resistance of said conductor.
5. The sensor of claim 4, wherein said test port comprises a
calibration port.
6. The sensor of claim 4, wherein said conductor comprises an
electric wire.
7. The sensor of claim 4, wherein said conductor is wrapped
helically around the conduit.
8. The sensor of claim 4, further comprising a resistor disposed
electrically in series with said conductor.
9. The sensor of claim 4, further comprising a resistance detector
coupled to said conductor, said resistance detector configured to
detect any deviation from said predetermined resistance.
10. The sensor of claim 1, wherein said coils of the same type
comprise sense coils.
11. The sensor of claim 10, wherein coils disposed on the same leg
are coaxial with one another.
12. A method for fabricating a sensor for detecting conductivity of
a fluid flowing through a conduit, said method comprising: (a)
providing a non-metallic conduit for the flow of a process fluid,
the conduit having an inlet and an outlet; (b) diverging the
conduit downstream of the inlet into first and second legs; (c)
re-converging the legs upstream of the outlet to form a fluid-flow
loop between the inlet and the outlet; (d) disposing at least one
first toroid configured as a first type coil about one of the first
and second legs; (e) disposing at least one second toroid
configured as a second type coil about one of said first and second
legs; (f) disposing at least one third toroid configured as a
redundant one of the first or second type coils about one of said
first and second legs, wherein coils of the same type are disposed
on opposite legs, in co-planar orientation with one another; (g)
selecting the first and second type coils from the group consisting
of drive and sense coils; and (h) configuring a connector to couple
the first, second and third toroids to an analyzer.
Description
TECHNICAL FIELD
This invention relates to conductivity sensors and more
particularly to electrodeless conductivity sensors configured to
detect the conductivity of process fluid flowing through a
conduit.
BACKGROUND INFORMATION
Throughout this application, various publications, patents and
published patent applications are referred to by an identifying
citation. The disclosures of the publications, patents and
published patent applications referenced in this application are
hereby incorporated by reference into the present disclosure.
Conductivity measurements of a chemical solution may be made by
applying a voltage across a pair of electrodes and immersing them
in the solution. The electric current passing through the system is
proportional to the conductivity of the solution. This technique,
however, is not optimal if the solution to be measured is
chemically incompatible with the metallic electrodes, e.g.,
resulting in chemical attack or contamination of the solution
and/or electrodes.
Another approach involves an electrodeless toroidal conductivity
measurement. In this approach, an electric transformer is
effectively created through the use of driver and sensor toroidal
coils surrounding a `core` formed at least partially by the
solution under test. The toroids are typically disposed within an
electrically insulative, magnetically transparent housing having a
fluid flow path which passes axially therethrough. The driver is
supplied with a voltage which induces an electromagnetic field in
the solution passing through the flow path, which then induces a
current in the sense coil. The induced current is proportional to
the conductivity of the solution being measured.
An example of such a toroidal conductivity sensor is disclosed in
Reese, U.S. Pat. No. 5,157,332. A commercial example of a similar
sensor is known as the 871EC.TM. invasive conductivity sensor
available from Invensys Systems, Inc. (Foxboro, Mass.). As shown in
FIG. 1, a section of such an electrodeless conductivity sensor 20
includes toroidal coils 11, 12, 13 encased in a housing 21, which
may be immersed in the fluid to be measured. The housing 21 defines
a central bore 19 which allows fluid to pass axially through the
toroids 11, 12, 13, without contacting them. The induction loop of
the `core` is completed by the process solution within which the
sensor is immersed.
Where a fluid to be measured is flowing through a conduit, it may
not be possible or desirable to immerse a sensor in the fluid. In
this event, driver and sensor toroidal coils may surround a pipe
carrying the liquid. A commercial example of such a sensor is known
as the 871FT.TM. (Invensys Systems, Inc.). However, in order for
induction to occur, an electrical loop must be completed outside
the coils, typically by clamping a metallic strap to metallic
portions of the pipe upstream and downstream of the toroids. A
drawback of this approach, however, is that metallic pipe portions
cannot be used when the process fluid attacks or is otherwise
incompatible with metals.
In an alternate approach, the induction loop may be completed by
the fluid itself, by providing a secondary flow path that bypasses
one or more of the toroids. An example of such a fluid loop is
disclosed in U.S. Pat. No. 2,709,785 to Fielden. A drawback of this
approach is that the limited cross section, relatively long length
and high resistance of the fluid itself, adds a net resistance to
the induced current which tends to adversely affect the sensitivity
of conductivity measurement. Approaches intended to enhance the
sensitivity of conductivity sensors include that disclosed by
Ogawa, in U.S. Pat. No. 4,740,755. Ogawa discloses toroids on a
fluid loop with dimensions calculated to "provide a low value for
the ratio of the length of fluid flow loop . . . to the cross
sectional area of the flow path, which in turn provides good
sensitivity." (Ogawa col. 2 lines 42-47). A drawback to this
approach is that Ogawa's toroids are taught to be coplanar and
physically separated in order to reduce leakage coupling between
the transformers. (Ogawa at col. 1, lines 34-38, col. 2 lines
47-52, col. 4, lines 49-55).
A need therefore exists for an electrodeless conductivity
measurement system that addresses one or more of the aforementioned
drawbacks.
SUMMARY
In accordance with one aspect of the invention, an electrodeless
conductivity sensor is provided for determining conductivity of a
process fluid. The sensor includes a non-metallic conduit which
diverges downstream of an inlet into first and second legs, and
re-converges upstream of an outlet, to form a fluid-flow loop
between the inlet and the outlet. First and second toroids, each
configured as either a drive or a sense coil, are disposed about
one of the first and second legs. A third toroid configured as
either a redundant drive or sense coil is also disposed about one
of the legs. A connector is configured to couple the first, second
and third toroids to an analyzer.
In another aspect of the invention, an electrodeless conductivity
sensor includes a non-electrically conductive fluid flow conduit
which diverges downstream of an inlet into first and second legs,
and then re-converges upstream of the outlet to form a fluid loop
between the inlet and the outlet. A housing encloses the legs.
Toroids configured as first and second type coils are disposed
about the legs. The first and second type coils are selected from
the group consisting of drive coils and sense coils. A toroid of
the first type is disposed between toroids of the second type on
each of the legs. In addition, at least one other toroid configured
as a sensor coil is disposed about the conduit outside of the fluid
loop. Shields are interspersed between the coils to magnetically
isolate the coils from one another. A calibration loop including an
electrical conductor extends through the toroids on the two legs,
and a leakage detector including an other electrical conductor is
disposed within the housing in spaced relation from the toroids.
The leakage detector is connectable to resistance measuring
means.
A further aspect of the invention includes an apparatus for
detecting leakage of process fluid from a fluid flow conduit. The
apparatus includes an electrical conductor disposed in
leakage-contacting relation to the conduit, the conductor having a
predetermined electrical resistance. A test port has terminals
coupled to opposite ends of the conductor, and is couplable to
resistance measuring means for measuring resistance of the sensing
conductor.
Yet another aspect of the invention includes a method for
fabricating a sensor for detecting conductivity of a fluid flowing
through a conduit. The method includes providing a non-metallic
conduit for the flow of a process fluid, diverging the conduit
downstream of an inlet into first and second legs, and
re-converging the legs upstream of an outlet to form a fluid-flow
loop between the inlet and the outlet. The method also includes
placing a drive toroid about one of the legs, placing a sense
toroid about one of the legs, and placing a redundant drive or
sense toroid about one of the legs. A connector is configured to
couple the toroids to an analyzer.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of this invention will
be more readily apparent from a reading of the following detailed
description of various aspects of the invention taken in
conjunction with the accompanying drawings, in which:
FIG. 1 is a cross sectional elevational view of a portion of an EC
sensor of the prior art;
FIG. 2 is an elevational view of an embodiment of the claimed
invention, with optional features shown in phantom;
FIG. 3 is an exploded view, with portions shown in phantom, of the
embodiment of FIG. 2;
FIG. 4 is a partially cross-sectional elevational view of an
alternate embodiment of the claimed invention, with optional
portions thereof shown in phantom;
FIG. 5 is a plan view of the embodiment of FIG. 4;
FIG. 6 is an exemplary wiring schematic of an embodiment of the
present invention; and
FIG. 7 is an exemplary wiring schematic of an alternate embodiment
of the present invention.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the
accompanying drawings that form a part hereof, and in which is
shown by way of illustration, specific embodiments in which the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that other embodiments
may be utilized. It is also to be understood that structural,
procedural and system changes may be made without departing from
the spirit and scope of the present invention. The following
detailed description is, therefore, not to be taken in a limiting
sense, and the scope of the present invention is defined by the
appended claims and their equivalents. For clarity of exposition,
like features shown in the accompanying drawings are indicated with
like reference numerals and similar features as shown in alternate
embodiments in the drawings are indicated with similar reference
numerals. Where used in this disclosure, the term "axial" when used
in connection with an element described herein, shall refer to a
direction parallel to the flowpath and/or downstream flow of the
process solution therethrough.
In a representative embodiment of the present invention, a fluid to
be measured flows through a conduit fabricated from a non
electrically conductive material. Toroidal coils surround the
conduit, without physically contacting the fluid. A voltage is
supplied to a driver coil, which induces a magnetic field in the
fluid flowing within the conduit. This magnetic field similarly
induces an electric current in a sensor coil.
A complete loop through which the magnetic field propagates is
formed by the fluid itself, via a secondary flowpath which diverges
from the primary flowpath of the conduit upstream from the
measuring toroidal coils, and reconverges with the primary flowpath
of the conduit downstream from the measuring coils. The toroidal
coils may be disposed on the primary flowpath, the secondary
flowpath, or both.
The instant inventors have recognized that the sensitivity of the
conductivity measurement tends to be adversely affected by the
distance the magnetic field must travel through the fluid loop. To
compensate for this, embodiments of the invention have been
provided with one or more redundant toroidal coils, wired in
parallel, to boost induction.
Particular embodiments may also include additional sensor coils
disposed upstream and/or downstream of the fluid loop. These
additional sensor coils may be wired in reverse phase relative to
the driver coils to cancel out stray electrical noise in the
system. In addition, a leak detector conductor may optionally be
disposed in proximity to the conduit. This conductor may be
fabricated from a material sensitive to the process fluid, and may
be helically coiled around the conduit, or simply supported
parallel to thereto. The conductor may then be connected to an
Ohmmeter, whereupon any change from a known baseline resistance,
such as may occur due to chemical attack by the process fluid,
would be indicative of a leak in the conduit.
Turning now to the figures, an embodiment of the present invention
includes conductivity sensor 200 as shown in FIG. 2. Process fluid
flows through conduit 202 in a downstream direction from an inlet
204 to an outlet 206. The conduit diverges at point 208 and forms
two flow paths, the primary flow path 210 and the secondary flow
path 212. The conduit then reconverges at point 209. The primary
flow path 210 and secondary flow path 212 form a fluid-flow loop
214.
In this embodiment, toroids 220, 222, and 224 are located on the
primary flow path 210. As described hereinabove, these toroids 220,
222, 224 surround conduit 210 and are physically and electrically
isolated from the process fluid flowing through conduit 210. In one
embodiment, the central toroid 222 is a sense toroid, and the outer
toroids 220, 224 are drive toroids. In another embodiment, the
central toroid 222 is a drive toroid, and the outer toroids 220,
224 are sense toroids.
For ease of explanation, the outer toroids 220 and 224 will be
designated as drive toroids, and the central toroid 222 will be
designated as a sense toroid, with the understanding that the
following discussion may also be applicable to the opposite
configuration in which the drive and sense toroids are reversed.
Electric current supplied to the redundant driver toroids 220, 224
creates a magnetic field which induces an EM field or current which
flows through fluid loop (core) 214. This induction similarly
induces a current in sense toroid 222, which is proportional to the
conductivity of the process fluid.
Use of primary and secondary flow paths 210 and 212 enables the
induction loop to be formed by the fluid itself, rather than via a
metallic strap as commonly used in the prior art. This enables
sensor 200 to measure the conductivity of fluids that tend to
attack or are otherwise incompatible with metallic fittings or
conductors. Moreover, the use of redundant toroids (either as a
drive or sense toroid) as shown, provides enhanced sensitivity
which compensates for the adverse affects on sensitivity otherwise
associated with relatively high resistance fluid-loop inductive
cores.
Optionally, embodiments of the invention may include one or more
additional toroids 230, 232, and 234 (shown in phantom) located
along fluid loop 214. For convenience, these additional toroids are
shown as disposed on secondary flow path 212, but may be
substantially anywhere along loop 214. While nominally any
combination of drive and sense toroids may be used, in a
representative embodiment, toroids 230 and 234 may be operated as
drive toroids, with toroid 232 as a sense toroid. These additional
toroids may be used in combination, e.g., by wiring them
electrically in parallel with respective ones of toroids 220, 222
and/or 224, to further enhance the induction via fluid loop
214.
In another variation of the instant invention, one or more
additional sensor toroidal coils 240, 242 may be disposed upstream
and/or downstream of fluid loop 214. These sensor coils 240, 242
may be wired in reverse phase with the other (on-loop) sense coils
222, 232, etc., to effectively cancel out electrical noise which
may be present in the conduit 210 outside fluid loop 214.
Turning now to FIG. 3, one set of three toroids, e.g., toroids 220,
222 and 224, is shown in an exploded view. As shown, toroids 220
and 224 may be connected in parallel to a source of electric
current via cables 360, 364, to function as drive toroids. Toroid
322 is connected by cable 362 to a conventional analysis apparatus,
such as the 875EC Series Analyzers or 870ITEC Series Transmitters
(Invensys Systems Inc., Foxboro, Mass.) which may be further
coupled to a conventional factory automation system.
As also shown, shields 350, 352, may be interspersed between the
toroids to help prevent the fields generated by the drive toroids
from interfering with one another and/or with the sense toroids. In
desired embodiments, these magnetic shields 350, 352 extend
circumferentially about conduit 302, while remaining physically and
electrically isolated from the process fluid flowing therethrough.
For example, in particular embodiments magnetic shields 350, 352
are centrally apertured discs, in the form of copper washers.
Ground wire 354 connects shields 350, 352 to one another, and to
ground.
Referring now to FIGS. 4 & 5, any of the aforementioned
embodiments may be disposed within a housing 469, to form an
enclosed conductivity measurement device shown at 400. In this
embodiment, driver toroids 420, 424 and sense toroid 422 are
coupled to a modular connector portion 470 to facilitate removable
connection to a transmitter or other data capture/calculation
device or system. Connector portion 470 may be nominally any
connector type known to those skilled in the art. A test port 476
is also shown, which may be coupled to opposite ends of a
calibration conductor 471 of known resistance, which forms a loop
passing through the toroids as shown. Calibration conductor 471 may
be used to calibrate device 400 by shorting the ends thereof (e.g.,
using a calibrator plugged into test port 476), and then operating
the device without process fluid in fluid loop 214. The output of
the sensor toroids may then be calibrated to match the known
resistance of conductor 471, as will be discussed in greater detail
hereinbelow. Those skilled in the art should recognize that this
calibration port/conductor, and any other aspects shown and
described with respect to a particular embodiment, may be applied
to any other of the embodiments described herein, without departing
from the spirit and scope of the present invention.
As also shown, an optional leak detection conductor 477 (shown in
phantom) may be provided. The conductor 477 may be disposed at
substantially any location likely to come into contact with process
fluid leaking from conduit 402. In the embodiment shown, conductor
477 may be disposed at any convenient location within housing 469,
such as at the lowest installed location thereof, i.e., at the
point at which any leaked process fluid would collect. In addition,
or alternatively, conductor 477 may be extended alongside, or
wrapped helically around conduit 402 as shown in phantom. This
latter approach may be particularly useful in embodiments not
having a housing 469.
Conductor 477 may be fabricated from a material sensitive to the
particular process fluid under test. For example, since many of the
embodiments described herein are intended to measure the
conductivity of process fluids such as caustic acids (e.g., HF,
HCl) that chemically attack various types of metals (e.g.,
aluminum), conductor 477 may be fabricated from such a metal. The
resistance of conductor 477 may then be monitored, e.g., via
terminals C & D (FIG. 6) of test port 476, to measure any
changes in resistance which may be indicative of fluid having
leaked from conduit 402 and contacted conductor 477. For example,
an increase in measured resistance may occur due to chemical attack
and an associated reduction in cross-sectional area of the
conductor 477.
As a further option, conductor 477 may also include a discrete
resistor 478 (shown in phantom) as desired to customize the
baseline resistance. A resistor 478 may be chosen to increase the
baseline resistance beyond the expected resistance of the process
fluid. Contact with any leaked process fluid of lower resistance
would tend to decrease the measured resistance at test port 476, to
indicate the presence of the leak. This configuration may be
particularly useful when measuring a process fluid that does not
chemically attack conductor 477, but is nevertheless incompatible
with metals, such as due to contamination/purity concerns.
Although leak detection conductor 477 and optional resistor 478 are
shown and described as incorporated within the various conductivity
sensors of the present invention, those skilled in the art should
recognize that it may be used independently and/or in combination
with nominally any type of fluid sensor, without departing from the
spirit and scope of the present invention. For example, leak
detection conductor 477 and/or resistor 478 may be incorporated
with various temperature detectors, pressure detectors,
conductivity sensors, pH sensors, ORP sensors, flow meters, and
combinations thereof. Commercial examples of such devices include
the 83 Series Vortex Flowmeters, I/A Series Pressure Transmitters,
134 Series Intelligent Displacement Transmitters, I/A Series
Temperature Transmitters, 873 Series Electrochemical Analyzers, and
the 871 Series conductivity, pH and ORP sensors all commercially
available from Invensys Systems, Inc. of Foxboro, Mass.
As also shown, a temperature sensor 480, such as a conventional
resistance temperature detector (RTD), may be physically coupled to
the conduit to detect the temperature of the process fluid, and
electrically coupled to connector 470.
Turning now to FIG. 6, sensor 200 or 400 may be wired by connecting
drive toroids 220, 224 (or 420, 424) to legs A and B of connector
470. Sense toroid 222 (422) may be connected to legs D and E of the
connector 470. The optional magnetic shields 250, 252 may be
connected to leg C of the connector. Temperature sensor or
thermosensor 480 may be connected to legs F, G, and H of connector
670.
Calibration conductor 471 extends from terminal A of the test port
676 through toroids 620, 622, 624, and returns to terminal B
thereof. Optional leak detection conductor 477 (shown in phantom),
with or without resistor 478, extends from leg C of port 476, into
leak-contacting proximity to the conduit, and in spaced relation
from the toroids, and returns to leg D of the calibrator.
FIG. 7 shows a wiring schematic of an embodiment substantially
similar to those shown and described hereinabove with respect to
FIGS. 2 & 4, in which the principal flow path 210, and
optionally, the secondary flow path 212, each include one drive
toroid and two sense toroids. As shown, drive toroids 720, 734 are
connected to terminals A and B of connector 470. Sense toroids 722,
724, 730, 732 are connected to legs D, E of connector 470. Copper
washers 350, 352, 354, 356 serve as magnetic shields between the
toroids and are grounded at terminal C of connector 470. RTD 480
serves as a thermosensing means and is connected to terminals F, G,
H of connector 470. Optional leak detection conductor 477 (shown in
phantom), which may include resistor 478, may be connected to
terminals C and D of test port 476 as shown.
Embodiments of the invention having been described, the operation
thereof will be discussed with reference to the following Table
I.
TABLE-US-00001 TABLE I 802 fasten conduit ends 204 and 206 in
process flow line 804 couple connector 470 to a data capture
device/processor 806 calibrate by shorting terminals A & B of
test port 810 activate drive coils 812 capture current of sense
coils 814 calculate measured conductivity value 815 map calculated
conductivity value to known conductivity of the calibration loop
816 disable calibration loop 818 initiate process flow 819 repeat
steps 810, 812 and 814, to generate conductivity values for the
process fluid. 820 Optionally monitor system for leakage
As shown, conduit ends 204 and 206 are fastened 802 in series with
a process flow line, and connector 470 is coupled 804 to a data
capture device/processor such as an analyzer of the type available
commercially from Invensys Systems, Inc., as discussed hereinabove.
The sensor may then be calibrated 806, e.g., using a conventional
calibrator coupled to test port 476, which shorts terminals A &
B thereof to provide a closed induction loop of known resistance as
described hereinabove. Thereafter, a current may be fed 810 to
terminals A & B of connector 470, to activate the drive coil(s)
in parallel with one another, to induce an EM field in the
calibration loop, and in turn, induce a current in the sense coils.
Since the sense coil(s) are similarly wired in parallel with one
another, a single current value may be captured 812 at terminals D
& E of connector 470. This captured current value may then be
used in a conventional manner to calculate 814 a measured
conductivity value. The calculated conductivity value is then
adjusted or mapped 815 to the known conductivity of the calibration
loop. Once calibrated, terminals A & B of test port 476 are
disconnected 816 from one another to disable the calibration loop,
and process fluid is permitted to flow 818 through the device.
Steps 810, 812 and 814 are then repeated 819, to generate
conductivity values for the process fluid. Optionally, the flow
conduit may be monitored 820 for leakage, by periodically checking
for any deviation from baseline resistance of leak detection
conductor 477 and/or resistor 478. As described hereinabove, the
use of parallel fluid flow paths provides a completely fluidic
induction loop that eliminates the need for any metallic conductors
to contact the process fluid. This, in turn, enables the
conductivity measurement of process fluids that are incompatible
with metals. In addition, the redundancy of drive and/or sense
coils serves to enhance induction within the fluidic loop for
improved measurement sensitivity and/or accuracy.
In the preceding specification, the invention has been described
with reference to specific exemplary embodiments thereof. It will
be evident that various modifications and changes may be made
thereunto without departing from the broader spirit and scope of
the invention as set forth in the claims that follow. The
specification and drawings are accordingly to be regarded in an
illustrative rather than restrictive sense.
* * * * *